How a tankless works | Tankless Pros Water Heaters | Phoenix, Az

How a tankless works

 

This description below of "How a tankless works" is based on the Navien NPE A2 Series tankless water heater our most popular tankless recommended for Arizona homes.

​

A gas tankless (on-demand) water heater, heats water only when a hot-water faucet or fixture is opened (hot-water demand), rather than storing and continuously reheating a tank of water. The Navien NPE-A2 series (Advanced models such as the NPE-180A2, NPE-210A2, and NPE-240A2) is a high-efficiency condensing design that uses dual stainless steel heat exchangers plus Navien’s patented ComfortFlow® system.

 

Basic Operating Sequence (Condensing Tankless)

Navien describes the process this way for its condensing units:

1. A hot-water tap opens (hot water demand) and water begins to flow.

2. The flow sensor detects the demand and calculates how much hot water is needed.

3. The electronic igniter activates.

4. The gas control valve opens to supply the correct amount of natural gas or propane.

5. The combustion fan and venturi mix air and fuel in the proper ratio.

6. The premix burner ignites and produces a controlled flame.

7. Incoming cold water is first preheated in the secondary heat exchanger by recovering heat from the hot exhaust gases.

8. The preheated water then flows into the primary heat exchanger, where the main burner brings it up to the set temperature.

9. The unit continuously monitors outlet temperature and modulates (adjusts) the flame size as needed.

10. On NPE-A2 models the heated water passes through the internal buffer tank.

11. Hot water is delivered to the fixture at the desired temperature.

 

All this is done in a fraction of a second, and because the unit only fires when there is flow, there is no standby heat loss like a traditional tank-type water heater.

 

Condensing Technology and Dual Heat Exchangers

The NPE-A2 is a condensing unit, this type of tankless technology operates at the highest energy efficiency levels compared to a non-condensing type tankless unit (older tankless technology). Note non-condensing tankless units are still made and are used in some applications.

 

Hot exhaust gases pass over the secondary stainless-steel heat exchanger, transferring residual heat to the incoming cold water. As the exhaust cools, water vapor in it condenses (hence the name), releasing additional latent heat. This is why these units reach high Uniform Energy Factors—up to 0.97 UEF.

​

• Primary heat exchanger: Main heating with the burner flame.

• Secondary heat exchanger: Recovers heat from exhaust for preheating.

• Both are stainless steel for corrosion resistance and durability (15-year heat-exchanger warranty in typical Arizona residential use).

​​

The cooled exhaust allows the use of relatively inexpensive PVC, (up to 75 feet with 2-inch pipe on many installations) instead of expensive stainless steel that some other manufactures use. 

 

ComfortFlow® System (Key NPE-A2 Feature)

The “A2” models include a built-in recirculation pump and a small insulated buffer tank (approximately 0.4–0.5 gallon).

 

This system:

• Reduces or eliminates the “cold-water sandwich” (brief bursts of cold water that can occur with frequent on/off draws).

• Allows the unit to operate effectively at very low flow rates.

• Enables recirculation of hot water through a dedicated return line or, with the optional NaviCirc® valve, through the existing hot-water supply lines—without needing a separate external pump or complex controls.

​​

The recirculation can be scheduled or activated on demand (HotButton option). When active it uses some extra energy, but it dramatically shortens the wait for hot water at distant fixtures.

 

Additional Performance Details

• Turndown ratio up to 15:1 — the burner can modulate from a very low minimum input up to full capacity (e.g., roughly 10,000–150,000 BTU/h on the NPE-180A2, higher on the larger models). This provides stable temperature even when demand changes.

• Electronic ignition (no standing pilot).

• EZNav™ multi-line backlit control panel for temperature, flow rate, status, diagnostics, and cascade setup.

• Field-convertible between natural gas and propane (dual venturi system).

• Cascade capability up to 32 units with Ready-Link® technology for larger demands.

• Compact wall-hung design (indoor or outdoor versions available).

 

In short: Cold water enters → flow is sensed → burner lights and modulates → water is preheated by exhaust heat in the secondary exchanger → brought to final temperature in the primary exchanger → optionally buffered and/or recirculated by the ComfortFlow system → delivered hot on demand with high efficiency and minimal waste. The dual stainless-steel exchangers and built-in recirculation/buffer distinguish the NPE-A2 from simpler non-condensing or basic tankless units.

 

For more tips, call Victoria Baysinger, at (602) 833-1533 for free advice & helpful hints

“Enjoy Hot Water Tonight”